Process of recovering zinc from ores.



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Be it known that we, F EDERICK lLAIsT and JAMns ORR ELTON, citizens of the United States, residing at'Anaconda, inthe county of Deerlodge and State of Montana, have invented certain new and useful Improvements in Processes of Recovering Zinc from Ores,

of which the following is a specification.

In a copending application Serial No. 104,083, filed June 16, 1916, we have pointed out that impure zinc-bearing solutions, such for example as those prepared. by leaching calcined zinc ores with dilute sulfuric acid,

may advantageously be purified by'agitating the solutions with an electrolytically deposited zinc sponge, either with or wlthout preliminary drying of the sponge. We have i reguline form. The process in its preferred embodiment is cyclical in character, and

may be carried out as follows 'llhe calcine from the roasting furnaces is leached with a dilute sulfuric acid solution in order to dissolve the zinc. As is hereinafter explained this acid solution, in arepetition of the process, is preferably the eiduent from the electrolytic-cells in which the zinc is deposited. The solution from the leaching operation is oxidized if. necessary, and. any ferric iron therein is precipitated by an excess of calcine, or by limestone, or in till ti ii any other approved manner. This precipib tation of iron may be accomplished-either before or after the filtration of the solution as may be desired.

The resultin, iron-free solution is new agitated with zinc dust or sponge for the removal of copper, cadmium and other-relatively electronega'tive impurities. For this treatment the zinc sponge prepared by the electrolysis of purified or partly purified sine solutions has been found especially ell- :tective, and we prefer therefore ts employ Specification of Letters Patent.

- surface.

PROCESS OF RECOVEBING ZINC FROM GEES.

-atented Feb. 5, lull.

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in this step of the process the zinc sponge which is obtained at a later stage of the" otherwise, under strictly non-oxidizing conditions.

. After filtering out the precipitated impurities a completely neutral solution is obtained, which is usually practically free from impurities, and is collected in storage tanks. From these tanks a part or all of the lytic cells in whichare suspended anodesof zinc, and cathodes which are advantageously of aluminum. In these cells conditions are maintained whereby a portion of the Zinc in solution flows through a series of, electro the solution is deposited in the form of sponge, the quantity thus deposited being" adequate for the primary purification of the electrolyte as described above. The best conditions for the deposition of sponge are a low voltage, and a cold and particularly a neutral solution. Under these conditions zinc dissolves from the anodes as rapidly as it is deposited at .the cathodes, thus maintaining the neutrality of the solution.

From these zinc sponge cells the solution flows to the regular depositing cells, being mixed if desired with purified solution from the storage tanks, and having added thereto a sufficient proportion of the return acid solution (the effluent from these depositing cells) to give the required, acidity. lln this second series of cells, the conditions are maintained for obtaining a reguline deposit of zinc. For this purpose we prefer an acidity of-about 5 per cent, thesolution being electrolyzed with-lead or other insoluble anodes at a temperatureof approximately '6. Suitable current conditions are a potential difference of 3 to 4: volts, with a current density of0.0215 to 0.0823 amperes per square centimeter of active electrode The eliluent solution from these cells usually contains from two to three. per cent. of zinc and from four to eight per cent. of free acid, and is used for leaching fresh quantities of calcine, the operation being therefore cyclical'in characte lit is to be noted that according to the pres-- ent process the sine sponge obtained by electrolytic precipitation from a solution which'has already undergone a primary its purification by means of finely-divided zinc, is itself used for this primary purification. Therefore the sponge-preci itating cells serve a double purpose: In the first place, they produce the sponge used for the primary purification; and in the second place,

. in producing this sponge, they subject the solution to a second and finalpurification, which under certain operating conditions may be highly important. For example, in case traces of copper or cadmium escape the primary purificationthey are e'flectively removed by the secondary treatment inthese eliminated as arsin) cells; and it furthermore appears that resid the ore with anacid solvent for zinc, preclpitating iron as a ferric compound, treating the resulting solution with finely-divided zinc to precipitate metals electronega'tive thereto,

' electrodepositingzinc in sponge form from portions of the treated solution, thereby furrocess of recovering zinc from ther purifying such portions of the solution and preparing finely-divided zinc for use in, therecipitating stage of the opera- 'tion, depositing .further quantities of zinc as reguline metal, and re-usingthe resulting acid solution in the leaching process.

, 2. In a process of recovering zinc from its ores, the steps which consist in-successively treating an impure-zinc-bearing solution with. finely divided zinc to precipitate metals electronegative to zinc, electrodepositing a portion of the zinc in the form of sponge from the thus-treated solution, and depositin further quantities of zinc from the puri ed solution as reguline metal. 3. In a process of recovering zinc from its ores, the steps which consist 1n successively treating an impurev zinc-bearing solution with finely-divided zinc to precipitate metals electronegative to zinc, depositing a portion of the zinc in the form of sponge from the thustreated solution by electrolyzing the same with anode surfaces of zinc, and depositing further quantities of zinc from the purified solution with insoluble anodes.

In testimony whereof, we afiix our signatures.

' FREDERICK LAIST. JAMES ORR ELTON. 

